Compressor unloader



May 3, 1949.

Filed Feb. 4, 1946 w. P. CAINE 2,469,224

COMPRES S OR UNLOADER 2 Sheets-Sheet 1 INVENTOR. W/LAMM P (AVA E Bibujz A TTORN Y May 3, 1949. V w, P, cA 2,469,224

' COMPRESSOR UNLOADER Filed Feb. 4, 1946 2 Sheets-Sheet 2 Z INVENTOR. l V/LLMM P Cllfif Patented May 3, 1949 UNITE STATES PA'ranr orrlc accaeza comraasson mvpoannn Will P. Caine, Birmingham-e, Ale. Application February d, 19%, Sendai No. 645,382 z e @laims. (pi. ace-24 This invention relates to an unloading device for an elastic fluid compressor and has for an object to provide a .device of the character designated which shall be adapted for use with a compressor driven at constant speed, and shall include means for lay-passing excess fluid to the .7 intake side of the compressor.

loader and the low pressure intake of the compressor when the compressor is shut down.

A more specific object of my invention is to provide a compressor unloader including a difierential piston for controlling the back flow of excess fluid to the intake of the compressor, together with variable means to control the actuating fluid for the piston.

Briefly, my invention comprises a differential piston in which both the larger and the smaller piston elements each comprises a valve, the smaller valve controlling the back flow of excess fluid to the intake of the compressor when it is in operation, and the larger being adapted to close the back flow of air from the receiver to the compressor when the compressor is shut down. The action or the differential piston is controlled by a spring biased valve operated responsive to receiver pressure, whereby when the receiver pressure reaches a predetermined value, the differential piston is actuated. The piston is further controlled by a constant leakage device, the amount of leakage through said device being adjustable, whereby the sensitiveness of control may be varied. When .the compressor is not in operation, and with pressure in the receiver, means are provided to gperate the differential piston to close off communication between the receiver and the compressor and to close the constant leakage device. By means of my improved mechanism, I have provided a very'sturdy, yet delicately adjustable unloading device which provides positive and sensitive control of the fluid flowing to the receiver and the excess fluid back to the compressor.

Apparatus embodying features of my invention is illustrated in the accompanying drawings, forming a part of this application, in which Fig. 1 is an assembly view showing my improved device in association with a compressor including high and low pressure cylinders;

Fig. 2 is a detail sectional view of the unloading valve; and

Fig. 3 is a wiring diagram illustrating the con- 2 nections to a solenoid operated valve employed with my invention.

Referring now to the drawing for a better understanding of my invention, 1 show in Fig. i a compressor including a low pressure cylinder it, and a high pressure cylinder ii, both being driven by a suitable motor M. Fluid being compressed is admitted to the low pressure cylinder it from an intake conduit 52 which may be provided with the usual filter i3. Fluid is discharged from the low pressure cylinder in through a discharge conduit i l, intercooler it, and conduit ii to the high pressure cylinder ii. Fluid is discharged from the high pressure cylinder ii through a conduit 68 and my improved unloading device, indicated generally by the numeral 59, and thence through a conduit at to a receiver 22. In normal operation, excess fluid is discharged from the unloading device it through a conduit 23 which connects to the intake conduit E2 of the low pressure cylinder iii.

My improved unloader valve embodies a housing connected to the compressor discharge conduit l8 through a passage 24, to the intake conduit 23 through a passage .28, and to the conduit leading to the receiver at 21. Within the housing of the unloader valve is a cylindrical chamber 28. A transverse division wall 29 extends across the housing and is provided with an opening 38 having a valve seat M on the upper side thereof. Below the opening 30 and in, line therewith, is an opening 32 leading to the passage 26 and provided with a valve seat 33 on the lower side thereof. Slidably mounted within the cylindrical chamber 28 is the larger end 34 of a differential piston which is mounted on a stem 35 extending down through the opening 32. The smaller end 36 of the difierential piston is mounted on the lower end of the stem 35 within the passage 26 leading to the intake conduit 23. The larger end 34 of the differential piston forms a valve which seats on the valve seat 3| when the piston is in its lowermost position. The smaller end 36 forms a valve which seats on the valve seat 33 when the differential piston is in its uppermost position as shown in the drawing. It will be seen that when the diflerential piston is in its uppermost position, communication between the compressor connection 24 and 26 is closed off by the smaller end 36 of the piston, whereas when the piston is in any position below that shown in the drawing. fluid may flow from the passage 24 past the .end 36 into the intake connection pasage 26.

Mounted over the valve housing just described is an operating valve 40 defining a chamber 31 connected through a passage 38' to a pilot valve chamber 39. Within the chamber 31 is a valve 4| controlling a passage 42 leading to the cylin-,

drical chamber 28 in which the differential piston 34 is mounted. The valve 4l' is biased toward an open position by means of a spring 43. Mounted over the valve 4| is a diaphragm 44 forming the upper wall of the chamber 31'and carrying a stem 46 which bears downwardly on the valve 4| to hold it closed until a predetermined pressure is reached in the receiver. A spring 41 bears against the opposite side of the diaphragm 44 and is adjustable by means of an adjusting screw 48 extending through a spring housing 49. The opening of the valve 4| is thus responsive to a predetermined receiver pressure.

Within the housing 40 is a passage communicating with the pilot valve chamber 39, and which has connected thereto a conduit 53 leading to the compressor intak connection 26. A conduit 56 connects the pilot valve chamber 39, opposite the passage 38, to the receiver connection 21.

Slidably fitting within the pilot valve chamber 39 is a pilot valve 51 of the piston type having enlarged ends 58 and 59 which, when the valve is in the position shown in Fig. 2 span the passage 38. Also, in that position, the lower, enlarged end 59 separates the passages 5| and 38.

- The valve 51 is provided with a stem 66, which is connected at its upper end to a solenoid 6|. When the compressor is in operation, the valve 51 assumes the position shown in Fig. 2 of the drawing and is held in that position by means of the solenoid 6|, which is energized in a manner to be described later, thus to hold the valve 51 in its uppermost position. When the compressor is not in operation, the solenoid 6| is de-ener ized and a spring 62 causes the valve 51 to move to its lowermost position. In its lowermost position, a valve 63 on the lower end thereof, covers a port 64 leading to the con-' duit 53 and thus closes ofi communication between the chamber '28 and the intake connection 26. The amount of opening of the port 64 is controlled by means of a plug valve 66 screwed into the lower end of the housing.

In Fig. 3 of the drawing, I show diagrammatically one way of operating the solenoid 6|. The motor M is shown provided with a field 61 and the solenoid 6|. is in-circuit with the field whereby, when the motor in operation reaches full speed the solenoid is energized.

The operation of my improved unloading apparatus is as follows: With the compressor in operation and with fluid under pressure being discharged through the conduit l8 to the unloading device through the connection 24, pressure acting on the .larger end 34 of the differential piston holds it in the upper'position shown in Fig. 2 of the drawing with the lower end 36 seated on the valve seat 33. Fluid being compressed thus fiows from the connection 24 through the opening 30 and out through the connection 21 to the receiver. Receiver pressure passes from the connection 21 through the conduit 56, around the valve 51 into the passage 38 leading to the control valve chamber 31. When the pressure within the receiver reaches a predetermined amount, it raises the diaphragm 44 and stem 46, permitting the spring 43 to open the valve 4|. This permits receiver pressure to flow past the valve 4| into the chamber 28 above the larger end 34 of the differential piston. As the. pressure on opposite sides of the larger end 34 of the dliferentialpiston approachesequilibrium, the piston moves downwardly, thus moving the valve 36 off its seat 33, thus connecting the inlet connection 24 with the connection 26 leading to the compressor intake conduit 23. At the same time, pressure from the chamber 28 flows through the passage 5| to the pilot valve chamber 39 and thence through the port 64 to the conduit 53 and the intake connection 26. So long as the compressor is delivering more fluid than is required to maintain the receiver 22 at its predetermined pressure, the action just described will continue and the smaller end 36 of smaller end 36 is again seated on its seat 33.

When the compressor is shut down, the solenoid 6| is de-energized and the spring 62 moves the pilot valve 51 to its lowest position, In this postion, the valve 63 covers the port 64 thus closing off communication between the chamber 28 and the intake connection 26. With the pilot valve 51 in its lowest position, receiver pressure from the connection 21 and conduit 56 flows into the chamber 28 through the passage 5| and around the pilot valve 51, thus causing the difierential piston to move to its lowest position with the larger end 34 seated on the valve seat 3|, thus closing off communication between the receiver and the intake connection 24.

When starting up the compressor after a shut down, the differential piston will be in its lowermost position, with the larger end 34 seated on the seat 3|. Until the motor is up to speed, the solenoid 6| will be de-energized and the valve 51 in its lowermost position. Fluid delivered by the compressor through the connection 24 will thus by-pass through the passage 32 to the intake connection 26. As soon as the motor is up to speed, the solenoid 6| is again energized and the pilot valve 51 is moved to its uppermost position as seen in Fig. 2 of the drawing.

From the foregoing, it will be apparent that I have devised an improved compressor unloader which is simple and sturdy of design, reliable in operation, and sensitive in its control.

terposed in the discharge conduit between the compressor and the receiver and comprising a housing communicating with the compressor and the receiver, and a conduit connecting the housing with the compressor intake, 2, diflerential piston and cylinder therefor disposed within the housing and normally subject to receiver pressure between its ends, a valve controlling communication between the housing and the compressor intake carried by the smaller end of the differential piston, a valve operable responsive to receiver pressure for admitting fluid from the receiver into the cylinder at the outer, larger end of the differential piston, a conduit affording communication between the receiver and the cylinder at the larger, outer end of the differential piston and a second valve in said conduit for controlling said communication, a Valve forming a part of the larger end of the differential piston and disposed, when the piston is moved responsive to fluid pressure-admitted to the cylinder through said by-pass conduit to close ofi communication through the housing between the receiver and the intake to the compressor.

2. In apparatus of the character describedincluding a fluid compressor having an intake conduit and a discharge conduit, the latter delivering compressed fluid into a receiver, an unloader interposed in the discharge conduit between the compressor and the receiver and comprising a housing communicating with the compressor and the receiver, and a conduit connecting the housing with the compressor intake, a'differential piston and cylinder therefor disposed within the housingv and normally subject to receiver pressure between its ends, a valve controlling communication between the housing and the compressor intake carried by the smaller end of the differential piston, a valve operable responsive to receiver pressure for admitting fluid from the receiver into the cylinder at the outer, larger end of the diiferential piston, a by-pass conduit affording communication between the receiver and the cylinder at the larger, outer end of the differential piston and a second valve in said conduit for controlling said communication, a valve forming a part of the larger end of the difierential piston and disposed when the piston is moved responsive to fluid pressure admitted to the cylinder through said by-pass conduit, to close off communication through the housing between the receiver and the intake to the'compressor, a second conduit affording communication between the cylinder and the compressor intake through said hollow stem, a valve for closing said communication, and means operable upon closing off communciation through the housing by the differential piston to close said last mentioned valve.

3. In apparatus of the character described including a fluid compressor having an intake conduit and a discharge conduit, the latter delivering compressed fluid into a receiver, an unloader interposed in the discharge conduit between the compressor and the receiver and comprising a housing communicating with the compressor and the receiver and a conduit connecting the hous-;

ing with the compressor intake, a differential piston and cylinder therefor disposed within the housing and normally subject to receiver pressure between its ends, a valve controlling communication between the housing and the compressor intake carried by the smaller end of the differential piston, a second valve operable responsive to receiver pressure for admitting fluid from the receiver into the cylinder at the outer, larger end of the differential piston, and means to adjust said second valve to open at a predetermined receiver pressure.

4. In apparatus of the character described including a fluid compressor having an intake con- 6 duit and a discharge conduit, the latter delivering compressed fluid into a receiver, an unloader interposed in the discharge conduit between the compressor and the receiver and comprising a housing communicating with the compressor and the receiver and a conduit connectingthe housing with the compressor intake, a differential piston and cylinder therefor disposed within the housing and normally subject to receiver pressure between its ends, a valve controlling communication between the housing and the compressor intake carried by the smaller end of the difierential piston, a second valve operable responsive to receiver pressure for admitting fluid from the receiver into the cylinder at the outer, larger end of the differential piston, a second housing joined to the first mentioned housing and having passages therein communicating with the receiver and said second valve, and with the cylinder at the outer end of the differential piston and the compressor intake, a pilot valve controlling said passages, an electric motor for driving the compressor, and a solenoid in circuit with the motor field for controlling the position of the pilot Valve.

5. In apparatus of the character described including a fluid compressor having an intake conduit and a discharge conduit, the latter delivering compressed fluid into a receiver, an unloader interposed in the discharge conduit between the compressor and the receiver and comprising a housing communicating with the compressor and the receiver and a conduit connecting the hous ing with the compressor intake, a differential piston and cylinder therefor disposed within the housing and normally subject to receiver pressure between its ends, a valve controlling communication between the housing and the compressor intake carried by the smaller end of the differential piston, a second valve operable responsive to receiver pressure for admitting fluid from the receiver into the cylinder at the outer, larger end of the differential piston, a second housing joined to the first mentioned housing and having passages therein communicating with the receiver and said second valve and with the cylinder at the outer end of the differential piston and the compressor intake, a pilot valve having an end portion disposed when the valve is in one extreme position to separate the two passages and when in the other extreme position to span the two passages and close off communication with the compressor intake, and means responsive to operation of the compressor to move the valve to the first mentioned extreme position.

6. In apparatus of the character described including a fluid compressor having an intake conduit and a discharge conduit, the latter delivering compressed fluid into a receiver, an unloader interposed in: the discharge conduit between the compressor and the receiver and comprising a housing communicating with the compressor, there being a conduit in the housing communicating with the compressor intake and discharge conduits and the receiver, a differential piston and cylinder therefor disposed within the housing and normallysubject to receiver pressure between its ends, a valve controlling communication between the compressor discharge and intake conduits carried by the smaller end of the differential piston, a second valve controlling communication between the receiver and the compressor'discharge on the larger end of the differential piston, and other valve means operable responsive to receiver pressure for admitting fluid from the receiver into the cylinder at the outer, larger end of the difierential piston.

7. In apparatus of the character described including a fluid compressor having an intake conduit and a discharge conduit, the latter delivering compressed fluid into a receiver, an unloader interposed in the discharge conduit between the compressor and the receiver and comprising a housing communicating with the compressor, there being a conduit in the housing communicating with the compressor intake and discharge conduits and the receiver, a differential piston and cylinder therefor disposed within the housing and normally positioned to pass fluid delivered by the compressor to the receiver, a valve controlling communication between the compressor discharge and intake conduits carried by the smaller end of the differential piston, a second valve operable responsive to receiver pressure for admitting fluid from the receiver into the cylinder at the outer, larger end of the differential piston, a third valve carried by the larger end of the 4 differential piston for controlling communication discharge conduits, the latter delivering compressed fluid into a receiver, an unloader interposed between the compressor discharge and intake conduits and comprising a housing, there being a passage in the housing communicating bodying a housing to which fluid under pressure is delivered through the discharge conduit, a conduit connecting the intake conduit with said unloader, a conduit connecting the housing to the receiver, a valve in the housing adapted when opento connect the intake and discharge conduits, a differential piston for opening said valve, and pressure regulating means to admit fluid under pressure from the receiver to said piston when pressure in the receiver reaches a predetermined value.

WILLIAM P. CAINE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,640,324 Hibbard June 3, 1930 1,847,229 Swanson et a1. Mar. 1, 1932 

